numpy 矩阵运算 | randn()函数

numpy.matlib.randn()是另一个在 numpy 中进行矩阵运算的函数。它从均值 0 和方差 1 的单变量“正态”（高斯）分布返回随机值矩阵。

Syntax : numpy.matlib.randn(*args)

Parameters :
*args : [Arguments] Shape of the output matrix. If given as N integers, each integer specifies the size of one dimension. If given as a tuple, this tuple gives the complete shape.If there are more than one argument and the first argument is a tuple then other arguments are ignored.

Return : The matrix of random values drawn from the standard normal distribution.

代码#1：

# Python program explaining
# numpy.matlib.randn() function
  
# importing matrix library from numpy
import numpy as geek
import numpy.matlib
  
# desired 3 x 4 random output matrix 
out_mat = geek.matlib.randn((3, 4)) 
print ("Output matrix : ", out_mat) 

输出 ：

Output matrix :  [[ 0.78620217  0.41624612 -0.28417131  0.1071018 ]
 [ 0.77645105  0.30858858 -1.98901344  1.25977209]
 [ 0.26279443 -0.41026178 -0.60834494  2.82552737]]

代码#2：

# Python program explaining
# numpy.matlib.randn() function
  
# importing numpy and matrix library
import numpy as geek
import numpy.matlib
  
# desired 1 x 5 random output matrix 
out_mat = geek.matlib.randn(5) 
print ("Output matrix : ", out_mat) 

输出 ：

Output matrix :  [[ 0.34973625  0.28159132  0.72581405 -1.17511692  1.96773952]]

代码#3：

# Python program explaining
# numpy.matlib.randn() function
  
# importing numpy and matrix library
import numpy as geek
import numpy.matlib
  
# more than one argument given
out_mat = geek.matlib.randn((5, 3), 4) 
print ("Output matrix : ", out_mat) 

输出 ：

Output matrix :  [[ 0.56784957  0.82980325  1.16683558]
 [-1.53444326 -0.27743273  0.65819067]
 [ 0.99654573 -1.20399432 -0.25603147]
 [ 1.74931585  0.58413453  1.67820029]
 [-1.25643231  0.21610229  0.21694595]]

注意：对于来自的随机样本$N(\mu, \sigma^2)$我们可以使用sigma * geek.matlib.randn(...) + mu 。
例如，制作一个 3 x 3 矩阵，其中的样本来自$N(3, 4)$ ：

代码#4：

# Python program explaining
# numpy.matlib.randn() function
  
# importing numpy and matrix library
import numpy as geek
import numpy.matlib
  
# So, here mu = 3, sigma = 2
out_mat = 2 * geek.matlib.randn((3, 3)) + 3
print ("Output matrix : ", out_mat) 

输出 ：

Output matrix :  [[ 4.04967121  0.26982021  2.3503067 ]
 [ 5.57757131  2.40051874 -0.84588539]
 [ 7.43715651  3.84004412  1.40514615]]